1. Field of the Invention
The present invention relates to a process of producing a polymer by polymerizing a monomer having an ethylenic double bond, and more particularly to a process of producing the polymer while effectively preventing polymer scale from being deposited on the inner wall surfaces, etc. of a polymerization vessel.
2. Description of the Prior Art
As a method of polymerizing a monomer having an ethylenic double bond, are known suspension polymerization, emulsion polymerization, solution polymerization, gas phase polymerization and bulk polymerization. In any type of the polymerizations, polymer scale is liable to be deposited on the areas with which the monomer come into contact during polymerization, such as inner walls, stirring equipment and so on of a polymerization vessel.
The deposition of the polymer scale results in disadvantages that the yield of the polymer and cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into a polymeric product, thereby impairing the quality thereof; and that removal of such polymer scale is laborious and hence time-consuming. Further, the polymer scale contains unreacted monomers and operators may be exposed thereto, which may cause physical disorders in the operators.
Heretofore, as a method for preventing polymer scale deposition on the inner wall and so forth, methods by which a polymer scale preventive agents comprising an amine compound, quinone compound, aldehyde compound or the like is coated on the inner wall, etc. of a polymerization vessel or methods by which such compounds are added to an aqueous medium for polymerization have been known (Japanese Patent Publication (KOKOKU) No. 45-30343 (1970)).
These methods can prevent the deposition of polymer scale if polymerization run is repeated within about 5 or 6 times; however, if the number of repetition of polymerization run exceeds 5 or 6, the scale preventive effect is weakened. That is, the scale preventive effect is poor in durability. Particularly, the scale preventive effect is adversely affected where a water-soluble catalyst is used and unsatisfactory industrially.
It is proposed in Japanese Pre-examination Patent Publication (KOKAI) No. 57-155201 (1982) to form a coating of a condensation product of an aromatic amine compound on the areas with which monomers comes into contact, such as the inner wall of a polymerization vessel. The formation of the coating of such a condensation product enables repetition of about 100 to 200 polymerization runs without deposition of polymer scale on the areas in the liquid phase, i.e., under the liquid surface inside the polymerization vessel. This effect is not lost even where a water-soluble catalyst is used,
However, polymer scale deposition is liable to occur on areas around the interface between the gas phase and the liquid phase which is located at the upper section of a polymerization vessel. Once polymer scale is deposited on an area around the interface between the gas phase and the liquid phase, the deposited scale will grow gradually as polymerization runs are repeated, and at last it is peeled from the inner wall, etc. and incorporated into the polymeric product. If the polymeric product containing the polymer scale is processed into formed products such as sheets or the like, the polymers scale causes increase in fish eyes in the formed products, lowering seriously the quality thereof.
Polymeric products obtained by polymerization are required to have a high whiteness. That is, when a polymeric product is formed into a sheet or the like without any addition of a coloring agent, the resulting formed product is more or less colored and such coloration, called initial coloration, is desired to be as low as possible. However, the coating comprising said condensation product of an aromatic amine compound disclosed in the Japanese Pre-examination Publication may be peeled or dissolved into a polymeric product, thereby lowering the whiteness or increasing the initial coloration thereof.